Download Leaf and Fruit Diseases of Tomatoes

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EC1864
Leaf and Fruit Diseases
of Tomatoes
Amy D. Timmerman, Extension Educator
Tomatoes are a common vegetable crop grown
throughout Nebraska and the United States. This publication provides symptoms, disease development and
management options available for common foliar and
fruit diseases affecting tomatoes.
Fungal Diseases
Early Blight
This fungal disease is caused by the pathogen Alternaria solani and is observed everywhere tomatoes are
grown. It starts at the bottom of the plant, infecting the
oldest leaves first.
Symptoms
This disease develops on the lower leaves of the plant
first and appears as brown to black circular spots 1/4 to
1/2 inch diameter with dark edges. These spots have a
“target-like” appearance because the fungus grows in
concentric rings as the spots enlarge (Figure 1). The tissue surrounding the spot may turn yellow, and spots can
coalesce to form large irregular blotches. Eventually the
infected leaves turn brown and defoliation occurs.
Figure 1. Tomato leaf with symptoms of early blight.
(Photo courtesy of Sarah Browning, Extension Educator,
University of Nebraska–Lincoln.)
water, or splashing rain when temperatures are between
75oF and 84oF. The spores germinate and penetrate the
leaf directly or enter through wounds. After initial infection, lesions can become visible in as little as two or
three days. Spores are produced in the new lesion when
it is approximately 1/10 of an inch in diameter.
Disease Development
Septoria Leaf Spot
Spores residing in the previous season’s debris in
soil, on seed or other Solanaceous hosts such as potato
(Solanum tuberosum), eggplant (S. melongena), horse­
nettle (S. carolinese), and black nightshade (S. nigrum)
are transmitted to susceptible leaves by either wind,
This fungal leaf spot can infect a tomato at any stage
of development but starts at the bottom of the plant
because it infects older leaves first. It is caused by the
fungus, Septoria lycopersici, and is a common disease of
tomato.
Extension is a Division of the Institute of Agriculture and Natural Resources at the University of
Nebraska–Lincoln cooperating with the Counties and the United States Department of Agriculture.
University of Nebraska–Lincoln Extension educational programs abide with the nondiscrimination
policies of the University of Nebraska–Lincoln and the United States Department of Agriculture.
© 2011, The Board of Regents of the University of Nebraska on behalf of the
University of Nebraska–Lincoln Extension. All rights reserved.
Figure 2. Tomato leaf with symptoms of Septoria leaf spot.
Figure 3. Tomato fruit with symptoms of anthracnose.
(Photo courtesy of Sarah Browning, Extension Educator
University of Nebraska–Lincoln.)
Symptoms
Anthracnose
Initially there are small, water-soaked circular spots
that appear on the underside of older leaves. These spots
are 1/16 - 1/8 inch in diameter with a dark brown margin
and gray or tan centers (Figure 2). Maturing spots will
enlarge­to 1/4 inch in diameter and may coalesce. With
mature spots, tiny black specks, which are the fruiting
bodies of this fungus, can be seen with the aid of a hand
lens. As leaves become severely infected, they become yellow in coloration, dry up, and defoliation can occur.
Anthracnose is caused by the fungus Colletotrichum
coccodes and is considered the most common ripe or
overripe fruit-attacking fungal pathogen.
Disease Development
The spores are released from the mature fruiting
bodies when temperatures range from 59oF to 80oF
with the optimal temperature of 77oF. Upon release, the
spores can move either by wind, water, splashing rain, or
insects, and by humans during pruning and harvesting.
When temperatures are optimal, spores can germinate
within 48 hours when moisture is available and a new
lesion can appear within five days. The tiny black specks
observed in the spot can be observed within 7 to 10 days,
and spores are being produced within 10 to 13 days after
spore germination. The moisture required for germination can occur during the summer months when relative
humidity is high for several hours.
Septoria overwinters on diseased plant debris that is
incorporated into the soil. It also survives on solanaceous
weeds such as seed horsenettle (Solanum caroinense) and
black nightshade (Solanum nigrum). This fungus can also
infect other vegetables grown in a garden such as potato
and eggplant.
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Symptoms
Symptoms, which do not become apparent until the
fruit begins to ripen, are initially small, circular indented
spots in the skin. The lesion continues to enlarge and
can increase to 1/2 inch in diameter and become more
sunken (Figure 3). The center of the lesion becomes
dark in coloration or concentric rings of dark specks
can develop­. The dark specks observed are the sporeproducing bodies of the fungus. However, when weather
conditions are moist, these black bodies will produce
large numbers of cream to salmon-pink colored spores.
Typically once spores are observed, the fungus has penetrated deeply into the fruit flesh and decay is occurring.
Eventually spotted fruits will rot completely due to the
colonization of other secondary fungi.
Disease Development
The fungus survives the winter on infected tomato
residue, in the soil and in seeds. Spores are spread to fruit
by rain splash or irrigation. When the weather is moist
and temperatures are between 55oF and 95oF, spores will
germinate and infect the ripening fruit.
Late Blight
Late blight is caused by the fungus Phytophthora
infestans­, which is considered a minor disease of tomato­
in Nebraska; however, it can be devastating when
weather­is conducive for disease development.
© The Board of Regents of the University of Nebraska. All rights reserved.
Symptoms
Figure 4. Tomato leaf with symptoms of late blight.
This pathogen can infect all parts of the tomato plant
and initially leaf symptoms are small dark, water-soaked
spots. These small spots can enlarge quickly and a white
mold can develop at the margins of the spot on the lower
leaf surface. Enlarged spots on the leaf give the plant a
frost-damaged appearance. Infected plants become­completely brown with shriveled leaves and stems (Figure 4)
within 14 days following initial symptoms when weather is
very favorable for disease develop­ment. Green or ripe fruit
also can become infected, initially appearing as gray-green
with water-soaked spots (Figure 5). The fruit spots enlarge
to affect half the fruit, turning the fruit dark brown with
complete rot (Figure 6).
Disease Development
Disease development is favored by moist weather
with cool nights (50-55oF) and moderately warm days.
When daytime temperatures are above 86oF, late blight
will not develop. The pathogen overwinters in dead
tomato­and potato (very susceptible host) vines from the
previous year. It also survives in potato seed tubers and
in infected tomato plants. The spores are spread by wind
and water splash.
Management of Fungal Diseases
Managing and preventing fungal diseases can be
successful through the use of a combination of several
cultural practices.
Figure 5. Tomato fruit with symptoms of late blight.
• Good sanitation in the fall and during the growing
season. Remove as much plant debris as possible,
and bury the remaining residue to promote decay
of the infested material. During the growing season,
remove infected leaves to reduce the amount of
inoculum­present to cause new infections.
• Plant certified disease-free seeds and transplants,
and plants with resistance.
• Rotate the position of tomatoes in the garden when
possible. Avoid planting eggplant, peppers, or potato
in the same garden area where tomatoes were grown
the year before.
• Avoid overcrowding plants in the garden. The strategy is to promote air movement through the plants
and allow the foliage to dry quicker.
Figure 6. Mature tomato fruit with severe symptoms and
rotting due to late blight infection.
© The Board of Regents of the University of Nebraska. All rights reserved.
• Apply water at the base of the plant to prevent water
splashing and minimize movement of spores to noninfected tissue. Also try to water during the morning
which will reduce the amount of time the leaves are
wet. Soaker hose irrigation is the optimum way to
water plants.
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Table 1. Fungicidesa available for early blight, septoria, anthracnose and late blight.
Anthracnose
Late
Blight
Commercial (C)/
Homeowner (H)
Use
X
X
X
C
X
X
X
X
C
Natria Disease Control (Bayer
Advanced)
X
X
X
X
H
Serenade® Garden (AgraQuest,
Inc)
X
X
X
H
Bravo Weather Stick (Syngenta)
X
X
X
X
C
Chlorothalonil 720 (Chem Nut
Inc)
X
X
X
X
C
Echo® 720 (Sipcam Agro USA,
Inc)
X
X
X
X
C
Equus® 720 SST (Makhteshim
Agan of North America, Inc)
X
X
X
X
C
Early May Fung-Onil Multipurpose Fungicide (Bonide
Products)
X
X
X
X
H
Fertilome Broad Spectrum Landscape and Garden Fungicide­(Voluntary
Purchasing­Groups Inc)
X
X
X
H
Fruit Tree, Vegetable and
Ornamental­Fungicide (Lawn
and Garden Products, Inc)
X
X
X
X
H
Ortho® Max Garden Disease
Control (The Ortho Group)
X
X
X
X
H
Ridomil Gold Bravo (Syngenta)­
X
X
X
X
C
Dragoon Dust with Cooper
(Bonide Products Inc.)
X
X
X
X
H
Cuprofix® Ultra 40 Dispress
(Cerexagri-Nisso LLC)
X
X
X
X
C
Earth-tone Garden Fungicide
(The Espoma Co)
X
X
X
X
H
Liquid Copper Fungicide
Concentrate­(Bonide Products
Inc.)
X
X
X
X
H
Copper Hydroxide Champ® WG (NuFarm
Americas­INC)
X
X
X
X
C
Kocide® 2000 (DuPont)
X
X
X
X
C
Fungicide Active
Ingredient
Azoxystrobin
Bacillus subtillis
Chlorothalonil
Copper
4
Early
Blightb
Septoria
Amistar (Syngenta)
X
Quadris (Syngenta)
Trade Name
© The Board of Regents of the University of Nebraska. All rights reserved.
Fungicide Active
Ingredient
Trade Name
Nu-Cop® 3L (Micro Flo
Company)­
Early
Blightb
Septoria
Anthracnose
Late
Blight
X
Commercial (C)/
Homeowner (H)
Use
C
Cyazofamid
Ranman® Fungicide (FMC
Agricultural­Products
Corporation)­
X
C
Dimethomorph
Acrobat 50WP (BASF
Chemical­Company)
X
C
Forum® (BASF Chemical
Company)
X
C
X
C
X
C
X
C
Famoxadone +
Cymoxanil­
Tanos® (DuPont)
X
X
Fenamidone
Reason® 500 SC Fungicide
(Bayer Crop Science)
X
X
Fluoxastrobin
Evito™ 480 SC
X
X
Hydrogen Dioxide OxiDate (BioSafe Systems)
X
X
X
X
C
Mandipropamid + Revus Top® (Syngenta)
Difenoconazole
X
X
X
X
C
Maneb
Maneb 80 WP Fungicide
(Cerexagri­)
X
X
X
X
C
Mancozeb
Dithane DF Rainshield (Dow
AgroSciences)
X
X
X
X
C
ManKocide® (DuPont)
X
X
X
X
C
Gavel 75DF (Gowan)
X
X
X
C
X
C
Phosphorous Acid Rampart® Fungicide (Loveland
Products, Inc)
X
Polyoxin D Zinc
Salt
Veranda™ O (OHP)
X
Propamocarb
hydrochloride­
Previcur® Flex Fungicide
(Bayer­Crop Science)
X
Pyraclostrobin
Cabrio® EG Fungicide (BASF
Chemical Company)
X
Pyrimethanil
Scala™ Brand SC Fungicide
(Bayer Crop Science)
X
C
X
X
X
C
X
C
C
This list is presented for information only and no endorsement is intended for products listed nor criticism meant for products not listed. Consult the product label for specific application rates and plant growth stage. Read the label carefully before making any application.
b
Product is labeled to manage that particular tomato disease.
a
© The Board of Regents of the University of Nebraska. All rights reserved.
5
• Mulch around the base of the plants to prevent
splashing soil and spores on leaves.
• Avoid working with plants when the foliage is wet to
reduce human movement of the pathogen.
• Control Solanaceous weeds, such as black nightshade
and horsenettle around the garden area.
• Fungicides can be used to manage these diseases.
Refer to Table 1 for fungicide active ingredients that
can be used on tomatoes.
Bacterial Diseases
Bacterial Spot
Bacterial spot is caused by Xanthamonas campestris
pv. vesicatoria and can infect tomato and pepper.
Symptoms
Symptoms on the leaves and stems are small circular
to irregular shaped lesions, up to 1/8 inch across (Figure­
7). Leaf symptoms are very similar in appearance to
Septoria leaf spot, however bacterial spot lesions do not
develop a grayish brown center. Typically a yellow halo
surrounds each spot which can coalesce causing leaves
to wither and turn brown. The most common symptom
observed is on the fruit. Green fruit is susceptible to
infection and symptoms initially start as small watersoaked spots. As the spots age, they enlarge up to 1/8 to
1/4 inch in diameter, becoming gray-brown and scabby
with sunken, pitted centers (Figure 8).
Disease Development
This pathogen overwinters on the surface of seeds, in
infected tomato or pepper debris, and in the soil. It also
is commonly carried on infected transplants. The bacterium is spread by water splashing. Infections are favored
by warm temperatures (68-95oF), high humidity, and
long dew periods.
Bacterial Speck
Bacterial speck is caused by Pseudomonas syrinage
pv. tomato. This tomato pathogen does not infect pepper,
eggplant, potato, or other Solaneceous crops.
Symptoms
Figure 7. Tomato leaf with symptoms of bacterial spot.
Figure 8. Tomato with symptoms of bacterial spot.
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Foliar symptoms consist of small (1/16 to 1/4 inch)
black spots that are slightly raised and have a yellow halo.
The symptoms on the fruit are the most distinct for this
bacterial infection. Fruit infections occur on young green
fruit and are slightly raised, 1/32 to 1/16 inch in diameter, and have well-defined margins (Figure 9). The raised
Figure 9. Tomato with symptoms of bacterial speck on the
leaves and green fruit. (Image courtesy of Ken Pernezny,
University­of Florida – IFAS Extension.)
© The Board of Regents of the University of Nebraska. All rights reserved.
lesions are typically numerous on the fruit but are very
superficial and can be scraped off with a fingernail.
Disease Development
The bacterial speck pathogen overwinters in seed, in
plant debris, in soil, and on other weedy hosts. Infection
is favored by temperatures of 55oF to 75oF, dew, and high
humidity. Major outbreaks often follow rainstorms that
cause injury to leaves and splash infested soil onto the
leaves.
Management of Bacterial Diseases
Managing and preventing bacterial diseases can be
successful through the use of cultural practices.
• Good sanitation in the fall and during the growing
season. Try to remove as much plant debris as possible and bury the remaining residue to promote
decay of infested material. During the growing season, remove infected leaves to reduce the amount of
inoculum that can cause new infections.
• Rotate the position of tomatoes in the garden when
possible. Avoid planting pepper in the same area
where tomatoes were grown the year before.
• Avoid overcrowding plants in the garden. The strategy is to promote air movement through the plants
and allow the foliage to dry quicker.
• Water at the base of the plant to prevent water
splashing to move bacterial cells to noninfected tissue. Also try to water during the morning which will
reduce the amount of time the leaves are wet. Soaker
hose irrigation is the optimum way to water plants.
• Purchase certified disease-free seeds and transplants.
Viral Diseases
Tomato Spotted Wilt Virus
Tomato spotted wilt virus (TSWV) is the most common viral disease of tomato in Nebraska. This virus is
transmitted primarily by four thrip species including
western flower thrips (Frankliniella occidentalis), tobacco
thrips (F. fusca), blossom thrips (F. schultzei), and onion
thrips (Thrips. tabaci).
© The Board of Regents of the University of Nebraska. All rights reserved.
Figure 10. Tomato spotted wilt virus causing yellow/
orange­ringspots on mature fruit.
Symptoms
Symptoms vary widely due to varying cultivar reaction and the age of the plants when infection occurs.
Young leaves may have a bronze appearance and can
later develop numerous small, dark spots. The growing
tips are severely affected by necrosis and stunted growth,
which may be confused with growth regulator herbicide
injury. The most characteristic symptom is on the tomato fruit: green fruit have mottled, light green rings with
raised centers, and mature fruit have distinctive yellow
and/or orange ringspots (Figure 10).
Disease Development
TSWV can be transmitted by seed, but thrips are
largely responsible for the movement of this pathogen
from infected hosts. Thrips acquire the virus only during
the larval stage of development. This virus also has been
reported to infect 174 different plant species including
potato, pepper, eggplant, pea, chrysanthemum, zinnia,
impatiens, bindweed, lambsquarter, and several others.
Thrips are able to feed on other hosts to acquire the virus
and then transmit it to tomatoes in the area.
Tobacco Mosaic Virus
Tobacco mosaic virus (TMV) is a virus that is distributed worldwide. This virus is seedborne, however it
is transmitted very efficiently by humans. Unlike tomato
spotted wilt virus, this virus is not spread by insects.
7
Symptoms
Plants infected by tobacco mosaic virus have leaves
that are mottled with light and dark green and occasionally have a fern-like appearance with the leaf edges
turned down. Overall the plants are stunted and are not
vigorous. Typically fruits do not show symptoms except for the reduction in fruit size and uneven ripening.
Occasionally fruits may develop internal browning or
“brownwall.” This symptom is observed in mature but
unripened fruit and usually involves the fleshy sidewalls.
This symptom has been attributed to a “shock reaction”
of the plant to the viral infection.
This publication has been peer reviewed.
Disclaimer
Reference to commercial products or trade
names is made with the understanding that no
discrimination is intended of those not mentioned
and no endorsement by University of Nebraska–
Lincoln Extension is implied for those mentioned.
Management of Viral Diseases
• Remove infected plants to prevent further spread of
the disease.
UNL Extension publications are available online at http://extension.unl.edu/publications.
• Control weedy hosts such as bindweed and lambsquarter.
• Separating vegetables from flower beds may reduce
the potential of infection but will not eliminate the
problem completely.
• Plant virus resistant tomatoes.
• In a greenhouse setting, monitor for thrips and
when populations become significant, using insecticides may be beneficial.
• Tobacco products can be carriers of the virus. Thus
tobacco users should wash their hands with soap and
water before handling plants to prevent accidentally
introducing the virus.
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